1. Field of the Invention
This invention relates to a CVD process for producing magnetic oxide films having sufficient growth induced anisotropy to support stable magnetic bubble domains therein, and an apparatus for achieving such films.
2. Description of the Prior Art
Chemical vapor deposition (CVD) has been a preferred technique for large scale manufacturing of single crystal films such as silicon and III-V compounds. These semiconductor crystals have been utilized in devices such as transistors and light emitting diodes. In addition to these uses, CVD has been used to produce magnetic films suitable for supporting stable magnetic bubble domains. In fact, magnetic garnet films were first prepared using CVD.
These CVD films had sufficient stress induced anisotropy to be able to support magnetic bubble domains. Typically, they were epitaxial magnetic garnet films grown on non-magnetic garnet substrates where the uniaxial anisotropy required for bubble domain formation was stress-induced. This stress results from the film/substrate lattice constant mismatch, as well as from thermal expansion mismatch resulting from a difference in thermal expansion coefficients of the film and the substrate.
The following references describe several CVD processes using different source materials to provide the gaseous constituents which are deposited on suitable substrates. Typically, they describe CVD processes for producing magnetic garnet films on non-magnetic garnet substrates. These references are:
1. United Kingdom patent No. 1,392,415
2. U.S. Pat. No. 3,429,740
3. U.S. Pat. No. 3,131,082
4. Besser et al, Mat.Res.Bull. Vol. 6, pp. 1111-1124, 1971
5. Sadagopan and Taylor, IBM Technical Disclosure Bulletin, Vol. 15, No. 2, July 1972
6. Cowher et al, Journal of Electronic Materials, Vol. 3, No. 3, page 621 (1974)
The CVD processes described in these references are all directed to producing anisotropy in magnetic bubble films by a stress mechanism. This is true regardless of whether the source materials are chlorides or organometallic compounds such as metal acetyl acetonates. Further, with the exception of the IBM Technical Disclosure Bulletin reference, the substrate temperature is high, generally in excess of 1000.degree. C. Still further, the oxygen stream which reacts with the gaseous source compounds is approximately 100% oxygen in these prior art references. None of these references describes or suggests a process for producing magnetic oxide films where growth induced anisotropy of sufficient magnitude is present to support stable magnetic domains, and in particular very small (i.e., less than 2 microns in diameter) stable magnetic bubble domains.
In the practice of the present invention, it has been recognized that CVD processes were not particularly suitable for the production of magnetic bubble domain films since the high temperatures used in these processes led to a number of difficulties including source degradation and reactor devitrification. These difficulties severely limit the manufacturing potential of CVD processes when magnetic bubble domain films are to be produced. As a consequence, liquid phase epitaxial growth of magnetic bubble domain films has superseded CVD for the growth of magnetic bubble garnet films.
For the production of magnetic bubble domains of very small diameters, large amounts of anisotropy are required. When a stress mechanism is used to produce this anisotropy, greater stresses are required to make films which support very small bubble domains. However, these large stresses can lead to cracking or wrinkling of the bubble films. For these reasons, CVD has been largely abandoned as a technique for producing magnetic bubble domain films.
The present invention seeks to eliminate the problems associated with prior art CVD processes so that CVD will once again become useful for the fabrication of suitable magnetic bubble films. To this end, the present invention seeks to provide a technique for using CVD processes in which the source of the necessary magnetic anisotropy is no longer a stress mechanism. Achievement of anisotropy in CVD bubble films without the need for stresses means that films can be grown to support very small stable bubble domains without undesirable mechanical properties, such as cracking or wrinkling of the bubble domain films.
In the course of numerous experiments, it has been found that certain steps can be undertaken to produce single crystal magnetic oxide films which will have sufficient perpendicular uniaxial anisotropy originating through a growth induced mechanism for support of stable magnetic bubble domains. The steps required in this process are critical and have to be followed in order to provide a sufficient amount of growth induced anisotropy. Additionally, these steps are important to produce smooth bubble films having uniform thickness and uniform magnetic properties throughout the film. Thus, the present invention in its broadest sense concerns a technique for providing, for the first time, chemical vapor deposition of magnetic films having growth induced anisotropy of an amount sufficient to support stable magnetic bubble domains therein.
Accordingly, it is a primary object of the present invention to provide a CVD process for producing magnetic films exhibiting growth induced magnetic uniaxial anisotropy of sufficient magnitude to support stable magnetic bubble domains therein.
It is another object of the present invention to provide a technique for CVD production of magnetic bubble domain films which are smooth and of uniform thickness, and exhibit growth induced magnetic anisotropy.
It is still another object of the present invention to provide magnetic bubble domain films having growth induced anisotropy by a CVD process where the growth rates are sufficiently low to allow very thin magnetic films to be deposited.
It is another object of the present invention to provide chemical vapor deposition of magnetic bubble domain films which support stable micron and submicron size bubble domains by a growth induced anisotropy mechanism.
It is another object of the present invention to provide chemical vapor deposited garnet films for supporting magnetic bubble domains therein, where the primary mechanism for producing anisotropy in these films is growth-induced.
It is another object of this invention to provide magnetic oxide films by chemical vapor deposition where the films exhibit growth induced anisotropy of sufficient magnitude to support stable magnetic bubble domains therein.